1. Field of the Invention
The invention relates in general to a protection apparatus and a multi-lamp driving system using the same, and more particularly to a protection apparatus with high sensitivity and low cost and a multi-lamp driving system using the same.
2. Description of the Related Art
Recently, there are some patents which disclose multi-lamp driving systems of large-size displays and current balancers thereof for detecting the malfunctioning lamps in order to reduce damage to the components. The disclosed multi-lamp driving system of the large-size display and the current balancer thereof cooperate with a protection circuit to provide better protection.
Please referring to FIG. 1, a conventional multi-lamp driving system is illustrated in FIG. 1. A ring balancer 110 disclosed in European Patent No. 1,671,521 is applied to the multi-lamp driving system 100. A protection circuit 120 is for malfunction protection (open circuit, short circuit or overload) of lamps. However, the ring balancer 110 is disposed at a high voltage end of the lamps L1˜Lk. When one or more of the lamps malfunction, the sensitivity of signals transmitted from stray capacitors C11˜Cn2 to detection node voltages V1˜Vk is insufficient. The protection circuit 120 malfunctions easily and is not able to output a protection signal S to control a driving circuit or shut down the power.
In a floating type current balancer disclosed in European Patent No. 1,581,030 or a Zaulas type current balancer disclosed in Japan Patent No. 2004-335443, a detection diode is used in a protection circuit. When one of the lamps malfunctions, a corresponding balance transformer in the current balancer generates extremely high voltage. Therefore, the detection diode has to sustain high voltage and therefore costs more. Furthermore, a large-size display needs a large area light source. In other words, more lamps are needed, and the number of detection diodes is increased accordingly. As a result, the cost is increased as well.
Therefore, it is very important to reduce the cost of the protection circuit and increase the sensitivity of detecting the malfunctioning lamp.